Hi... Welcome to HEALTHCARE MAGIC.. I have gone through your query and can understand your concerns... As per your complain difficulty in opening mouth with a history of tobacco chewing seems to be due to Oral Submucous Fibrosis in which there is formation of thick fibrous bands below the mucosa of the cheeks leading to stiffeness and reduced mouth opening.. There is also atrophy of the mucosa and along with it there is inflammation and burning sensation.. It is a pre cancerous condition and needs immediate medical attention and you should immediately stop smoking also as well as tobacco habit.. The pain in mouth on smoking seems to be burning pain and is due to heat causing irritation as well as the cheeks have stiffened so inward pressure on cheeks while smoking is also causing pain.. You should consult an Oral Physician and get evaluated and he/she can do a thorough clinical evaluation and advise you to do topical application of steroids and hyluronidase as it will help in reducing inflammation as well as breaking the adhesion between the fibres.. Anti-oxidants like Lycopene can also be advised.. Intra-lesional injections of steroid and hyluronidase can also help.. Mouth opening exercise like trying to open mouth under pressure and blowing cheeks has to be done 3 to 4 times a day.. Avoid hot and spicy food.. Completely quit smoking, tobacco chewing and alcohol intake as it can convert into oral cancer if care is not taken.. Hope this information helps.. Thanks and regards. Dr.Honey Nandwani Arora.